Perovskite-type structures are formed by ABX.sub.3 -type compounds where A atoms replace some of the X atoms in close-packed cubic layers and the B atoms fit in the sites octahedrally coordinated X atoms. Because of the flexibility of the perovskite structure with regard to substitution of a wide range of cations as well as modification of the structure itself, perovskites have proved useful for many applications. For example, U.S. Pat. No. 4,482,644 to Beyerlein et al. teaches oxygen-deficient barium-containing perovskites for use in oxidative dehydrogenation reactions.
Also, the perovskite structure has been modified to produce a two-dimensional structure in which additional cations separate perovskite-like layers. Such materials include Bi.sub.2 MoO.sub.6, which has been used in oxidation catalysis. See "Chemistry of Catalytic Processes", by B. C. Gates, J. R. Katzer and G. C. A. Schuit, McGraw-Hill, 1979, Chapter 4.
Furthermore, a series of perovskite-type compositions, represented by the formula M[Ca.sub.2 Nb.sub.3 O.sub.10 ] where M is Li, Na, K, Rb, or Cs, have been synthesized. See M. Dion, M. Ganne and M. Tournoux, Mat. Res. Bull. 16, 1429, 1981. These compositions are layered inorganic oxide structures wherein each layer is three Nb-oxygen octahedra thick. Such compositions are an example of a general type of structure which may be written M[A.sub.n-1 B.sub.n O.sub.3n+1 ] where the contents of the parenthesis are the perovskite-like layer and M is the charge balancing interlayer cation.
Compositions represented by the above formula where M is one or more of K, Rb, Cs, NH.sub.4, Tl, Ag, and hydrogen; A is one or more mono-, di-, or trivalent cations selected from the group consisting of Groups 1a, 2a, and 3b and the lanthanides, B is one or more transition metals selected from Re, and Groups 4b, 5b, and 6b of the Periodic Table of the Elements and n is an integer from 3 to 7, with the proviso that when n is equal to 3, and M is not hydrogen, B cannot be Nb, are described in a co-pending application U.S. Ser. No. 716,039, filed Mar. 26, 1985, and incorporated herein by reference.
Although perovskite-type compositions have been developed for various uses, there still exists a need in the art for the development of additional perovskite-type compositions.